Without limiting the scope of the present invention, its background will be described in relation to exploratory subterranean well operations, as an example.
As used herein, the words “comprise”, “have”, “include”, and all grammatical variations thereof are each intended to have an open, non-limiting meaning that does not exclude additional elements, steps, or embodiments. Furthermore, it should be understood that as used herein, “first”, “second”, “third”, etc. are arbitrarily assigned and are merely intended to differentiate between two or more elements, devices, embodiments, etc., as the case may be, and does not indicated a specific sequence, nor should be viewed as a limiting sequence. Furthermore, it is to be understood that the mere use of the term “first” does not automatically imply that it should be followed by a “second” or for that matter a “second by a “third”.
As used herein, a “fluid” is a substance having a continuous phase that tends to flow and to confirm to the boundaries of the vessel containing it. A fluid can display the properties of a liquid or a gas, depending on where, based on its composition, temperature and pressure, it falls on the gas-liquid continuum.
From simple beginnings, the search for oil reserves has moved into more remote locations and more technically demanding reservoirs and environments. Exploratory wells are often drilled with the goal of finding new hydrocarbon reserves, identifying the nature of the reserves, and then verifying their economic viability. Consequently, after a well has been drilled and underground hydrocarbon bearing strata have been identified, it is desirable to determine the physical characteristics of the strata in question and also the chemical characteristics of the hydrocarbon in place. The physical characteristics provide invaluable clues as to the extent of the reservoir and how fast it can be made to produce its hydrocarbon content. The chemical characteristics are invaluable in defining the monetary value of the hydrocarbon reserves as also the best mechanism by which the recovered reserves can be handled and further processed. Both the physical and chemical characteristics are invaluable pieces of information for defining the monetary value that can be assigned to a prospective discovery.
Numerous pieces of equipment and methodologies are available and well known to those active in the industry for determining the physical properties of a reservoir. These include the extensive suite of tools available during Measurement while Drilling (MWD) and Logging While Drilling (LWD) operation, Wireline Formation Testing (WFT) operations, Production Logging (PL) operation, and Surface Well Testing (SWT) operations including methodologies such as pressure drawdown testing, gamma-ray logging, neutron density logging, MRI logging, etc. For the sake of brevity these will not be further discussed, though an absence to do so should not be viewed as a limitation to this disclosure.
A detailed understanding of the reservoir fluid including its chemical description may be viewed as perhaps the most significant aspect of any well test operation. A sample of the reservoir fluid is invaluable for undertaking a detailed laboratory PVT analysis, where the initials PVT stand for Pressure, Volume, and Temperature. A representative reservoir sample is also crucial for generating a detailed chemical analysis of the hydrocarbon phase. For these and many other reasons it should be readily apparent to those familiar with the oil industry that collecting and recovering a representative sample of reservoir fluid is a crucial first step in defining the economic viability of a newly discovered hydrocarbon reservoir.
There are a number of opportunities during the exploratory and production cycle when a reservoir sample can be collected. Recent technological developments have made it possible for hydrocarbon samples to be collected as early as the drilling phase. During drilling operations samples can be collected in samplers associated with the drill string. After the conclusion of the drilling phase and while the drilled borehole is still an open hole, namely exposed formation rock, samples can be collected during traditional Wireline Formation Testing (WFT) operations. During WFT a number of tools directed at delivering a better understanding of the physical and chemical nature of the reservoir are introduced into the borehole via wireline. Included in this tool string is a set of samplers for collecting bottomhole samples.
Once casing is set and the openhole is cemented, a Drill Stem Test or DST can be undertaken. During a DST operation samples can be collected on pipe or tubing by incorporating carriers specifically designed for carrying a multiplicity of samplers from the surface to the subterranean zone of interest on the work string. A cased hole environment also affords numerous opportunities to run a set of production logging tools on e-line or wireline, which offers yet another excellent opportunity to collect samples of the reservoir fluids.
The sample collecting process itself is complicated and requires a number of distinct and necessary steps. First a subterranean zone of interest needs to be identified that would warrant the expense of undertaking a sampling operation. Next, a sample collection devise has to be brought adjacent to or in the vicinity of the subterranean zone of interest. With the sampler at location some mechanism is needed to trigger the sampler at the correct instance during some specific static or flow period appropriate to the testing being undertaken of the subterranean zone of interest. Once the sampler is triggered the sample should be collected in a controlled fashion so as to minimize the possibility of the sample flashing two phase. Once the sample collection has been completed, the sample has to be locked in place in the sampler, and simultaneously a high pressure charge of gas, usually nitrogen, is released against the sample to exert pressure on the sample and keep it single phase during recovery to the surface. At the surface the sample is usually transferred, again at high temperature and pressure, into long term storage bottles.
Almost exclusively, a sample is collected ahead of a moving piston located in a tubular section. Preserving the integrity of the sample during the collection phase requires that the movement of the piston be slowed down to prevent the sample from flashing to two phases the instant the sample's tubular section is exposed to the pressurized fluid phase to be sampled. Slowing the movement of the sample collecting piston is most easily accomplished by the simple expediency of incorporating some non-interacting fluid, usually referred to as a displacement fluid, on the backside of the piston, namely the side opposite to where the sample will collect. As a consequence, as the sample enters the tubular section on one side of the sample piston causing it to be laterally displaced, this lateral movement of the piston will result in a corresponding lateral displacement of the displacement fluid. If the lateral displacement of the displacement fluid is further constrained by forcing it through a very fine constriction or choke, then the resulting very slow movement of the piston due to the restriction of the movement of the displacement fluid is successful in delivering a single phase sample where flashing has been mostly eliminated. Furthermore, it should be readily obvious to one familiar with the art, that the very presence of the displacement fluid will require that the sampler be equipped with some low pressure dump chamber into which the displacement fluid can be ejected while the sample is being collected, and where the displacement fluid will stay stored during the entire sample collection, recovery to the surface, and subsequent storage until such time that the sample is transferred out of the sampler for further analysis.
Once the sample has been collected, it is necessary that it be immediately brought in contact with a high pressure nitrogen charge in order to bring the sample pressure up to some desirable value necessary for the sample to stay single phase during recovery to the surface and subsequent transportation and storage. Consequently, each sampler must be connected to a high pressure nitrogen source, to which end each sampler can have its own nitrogen source, which is by far the more prevalent design, or, as is seen in some very unique cases, there can be a common nitrogen source for more than one, or even all the samplers. Irrespective of the exact design, it is imperative that the pressure and volume of the nitrogen source be such that it will successfully maintain the sample pressure at least 2000 psi above and preferably even higher than the pressure at which the sample was collected, and maintain this high pressure during the entire subsequent history of the sample.
To reiterate, a successful sampling operation as conventionally undertaken requires some device rated for high pressure and temperature service which is equipped with a plurality of associated chambers and mechanisms such that when said device is brought alongside a subterranean formation of interest and triggered or activated, it will allow the fluid contained in the subterranean formation of interest to enter and gather in the appropriate receptacle. Furthermore, the entry of the said reservoir fluid into the said receptacle is deliberately controlled by the slow drainage of a displacement fluid from the receptacle receiving the sample into some immediately or closely associated chamber specifically included for the purpose of receiving the displacement fluid. The controlled movement of the displacement fluid is most effectively implemented by forcing the displacement fluid to flow through a restrictive choke as it transitions between the two aforementioned chambers.
Once the sample has been collected it is necessary that the sample be locked in place to trap it so it is contained for further transportation and handling. Simultaneously, a source of high pressure gas, preferably nitrogen, contained in a chamber either adjoining the sample receptacle or in close proximity to the sample receptacle, is brought in indirect communication with the collected sample so as to take the pressure of the sample at least 2000 psi above the pressure at which it was collected and keep it at this high pressure during the subsequent recovery to the surface.
All of this requires a number of intricate parts that must work in precise unison if the sampling step is to be successful. Consequently, it should be obvious to one well versed in the sampling art that there is a need for a sampler of simpler design that is easier and safer to operate and would deliver a more reliable performance than is presently available.